How to create a 3D model of an object and then put it on the Internet in a 3D viewer
This is fairly easy to do if you are using the Blender in combination with Sketchfab since there is an Addon that is included with Blender which sends the model directly to the website for you.(Although it can be buggy so I'll show how to do it without the Addon) 

At the time of writing, the free version of SketchFab allows you to upload .blend files that are a maximum of 50MB.

When the model is ready to be uploaded, you can pack all the textures individually or write a script that can iterate through all the textures and pack them automatically.  Once this is done then the .blend file will contain copies of the images.
This will be important for loading the scene file to Sketchfab, otherwise you can load them manually afterwards.



Next, go to the SketchFab website and locate the blue Upload button and then use the directory menu to select the .blend file that you would like to upload.



It's that simple to load a model, here it is shown in the interactive 3D viewer.



Now if you want to embed the model and viewer into a website click the Embed button and copy the contents of the mini popup dialogue.



Now paste this into the HTML code of your website as shown in the following image.



Here's what the page looks like after the code is embedded.  btw, the low quality banding is from the animated .gif, not sketchFab or Blender.



There is a page here that has some extra information on preparing the material so it will function correctly with exporters/SketchFab.

Exporting cycles rendered models to be used in opengl